Lithium batteries: a new tool in solid state chemistry

Lithium batteries are being intensively studied owing to the considerable challenge they represent for applications. From a fundamental point of view, the shape of the charge/discharge curves gives information on all the structural and physical properties modifications which occur during the intercalation/deintercalation process. Moreover, the electrochemical reaction is a way of synthesising metastable materials which cannot be obtained by classical methods. The ease of monitoring very accurately either the cell voltage (oxidation state of the material) or the number of electrons transferred (lithium content in the material) makes lithium batteries a new very convenient tool for the solid state chemist. Typical examples are presented.     

LiFePO4/C复合材料制备过程中碳源及碳包覆方法的研究进展

LiFePO4以其价格低廉、稳定性好、循环性能好和无毒等优点,有望成为下一代锂离子电池的正极材料,但是LiFePO4电导率低和锂离子扩散系数小限制了它的实用化。碳包覆作为一种非常有效的导电改性方法,受到极大关注。在碳包覆中采用不同的碳源和不同的碳包覆方法,对LiFePO4的电化学性能影响不同。结合国内外的研究现状,综述了LiFePO4/C复合材料制备过程中不同碳源以及不同的碳包覆方法对其电化学性能影响的研究进展。     

石墨层间化合物GICs的形成机理探讨

将ＧＩＣｓ形成过程划分为熔融、活化、扩散和成键等阶段,分析了各阶段反应的主要影响因素,以氯化铜、氯化镍、ＧＩＣｓ的合成实验为基础,根据ＳＥＭ对石墨膨胀前后,插层后的形貌分析,以及膨胀石墨合成ＧＩＣｓ反应前后体积变化分析,认为ＧＩＣｓ的形成过程中,主要有三个机制起作用：     

Orientation‐Dependent Intercalation Channels for Lithium and Sodium in Black Phosphorus

Black phosphorus (BP) with unique 2D structure enables the intercalation of foreign elements or molecules, which makes BP directly relevant to high‐capacity rechargeable batteries and also opens a promising strategy for tunable electronic transport and superconductivity. However, the underlying intercalation mechanism is not fully understood. Here, a comparative investigation on the electrochemically driven intercalation of lithium and sodium using in situ transmission electron microscopy is presented. Despite the same preferable intercalation channels along [100] (zigzag) direction, distinct anisotropic intercalation behaviors are observed, i.e., Li ions activate lateral intercalation along [010] (armchair) direction to form an overall uniform propagation, whereas Na diffusion is limited in the zigzag channels to cause the columnar intercalation. First‐principles calculations indicate that the diffusion of both Li and Na ions along the zigzag direction is energetically favorable, while Li/Na diffusion long the armchair direction encounters an increased energy barrier, but that of Na is significantly larger and insurmountable, which accounts for the orientation‐dependent intercalation channels. The evolution of chemical states during phase transformations (from Li_xP/Na_xP to Li₃P/Na₃P) is identified by analytical electron diffraction and energy‐loss spectroscopy. The findings elucidate atomistic Li/Na intercalation mechanisms in BP and show potential implications for other similar 2D materials.     

掺杂型炭材料在锂离子电池中的应用

对五种掺杂型炭材料的结构特征及其在锂离子电池中的嵌入机理作一综述,同时提出,除了炭材料的改性以外,硼、硅、磷和矾等四种元素在炭材料中的掺杂也将是未来锂离子电池发展的方向。     

Manipulate the Electronic and Magnetic States in NiCo2O4 Films through Electric‐Field‐Induced Protonation at Elevated Temperature

Ionic‐liquid‐gating‐ (ILG‐) induced proton evolution has emerged as a novel strategy to realize electron doping and manipulate the electronic and magnetic ground states in complex oxides. While the study of a wide range of systems (e.g., SrCoO_2.5, VO₂, WO₃, etc.) has demonstrated important opportunities to incorporate protons through ILG, protonation remains a big challenge for many others. Furthermore, the mechanism of proton intercalation from the ionic liquid/solid interface to whole film has not yet been revealed. Here, with a model system of inverse spinel NiCo₂O₄, an increase in system temperature during ILG forms a single but effective method to efficiently achieve protonation. Moreover, the ILG induces a novel phase transformation in NiCo₂O₄ from ferrimagnetic metallic into antiferromagnetic insulating with protonation at elevated temperatures. This study shows that environmental temperature is an efficient tuning knob to manipulate ILG‐induced ionic evolution.     

Intercalation of Layered Materials from Bulk to 2D

Intercalation in few‐layer (2D) materials is a rapidly growing area of research to develop next‐generation energy‐storage and optoelectronic devices, including batteries, sensors, transistors, and electrically tunable displays. Identifying fundamental differences between intercalation in bulk and 2D materials will play a key role in developing functional devices. Herein, advances in few‐layer intercalation are addressed in the historical context of bulk intercalation. First, synthesis methods and structural properties are discussed, emphasizing electrochemical techniques, the mechanism of intercalation, and the formation of a solid‐electrolyte interphase. To address fundamental differences between bulk and 2D materials, scaling relationships describe how intercalation kinetics, structure, and electronic and optical properties depend on material thickness and lateral dimension. Here, diffusion rates, pseudocapacity, limits of staging, and electronic structure are compared for bulk and 2D materials. Next, the optoelectronic properties are summarized, focusing on charge transfer, conductivity, and electronic structure. For energy devices, opportunities also emerge to design van der Waals heterostructures with high capacities and excellent cycling performance. Initial studies of heterostructured electrodes are compared to state‐of‐the‐art battery materials. Finally, challenges and opportunities are presented for 2D materials in energy and optoelectronic applications, along with promising research directions in synthesis and characterization to engineer 2D materials for superior devices.     

Synthesis and characterization of poly(ionic liquid)-grafted silica hybrid materials through surface radical chain-transfer polymerization and aqueous anion-exchange

Poly(ionic liquid)-grafted silica materials were firstly synthesized by polymerization of 1-vinyl-3-butylimidazolium bromide as a new ionic liquid monomer on mercaptopropylated silica by surface radical chain-transfer polymerization. The bromide counterion was exchanged with three other inorganic anions including tetrafluoroborate, hexafluorophosphate, and trifuoromethanesulfonate through simple aqueous anion-exchange reaction. The obtained poly(ionic liquid)-grafted silica materials were characterized by elemental analysis, infrared spectra, thermogravimetric analysis, and X-ray fluorescence. The wettabilities of the materials with different counterions were verified by static water contact angle measurement. This kind of new materials may have some potential in applied fields such as used as a catalyst, an extractant, a chromatographic stationary phase, etc.     

Electrical properties of lithium intercalated p-type GaSe

We have studied the intercalation reaction of p-type GaSe with n-butyl lithium in hexane solution through the time dependence of the electrical resistivity, and by Hall effect measurements. The electrical properties as a function of temperature have also been examined. Li_xGaSe resistivity is increasing as x is increased. The large variation of the resistivity is mainly attributed to the variation of the free carrier concentration in the host material. Lithium intercalation causes a compensation of GaSe, and the semiconducting character is conserved.     

A study of CdS as a solid electrolyte for a thin film galvanic cell

This work is a continuation of our previous work in which it was reported that vacuum-evaporated CdS, when sandwiched between an aluminium electrode and a catalytic electrode such as silver, shows a galvanic effect. Cells of the type Al/CdS/M (where M  Ag, Cu or Au) were made by vacuum evaporation. The ionic conductivity of the CdS films was determined using the d.c. polarization technique. The ratio of ionic to electronic conductivity was calculated and was observed to have a minimum value of 1:1. The increase in the cell voltage and the decrease in its internal resistance with increasing temperature were studied. An Arrhenius plot of cell resistance gave an activation energy of 0.82 eV for sulphur ion hopping. A possible reaction mechanism of voltage generation is described in terms of the ionic conductivity of CdS films and the electrochemical effects at the interface between the CdS and the electrode materials. The decrease in the cell voltage with ambient air pressure is compared with the theory. The photoeffect suggest that CdS is behaving partially as an electronic photoresistor.     

磷酸铁锂正极材料改性研究进展

磷酸铁锂(LiFePO4)是绿色环保的锂离子动力电池正极材料。但由于材料自身电子和离子传导率差、堆积密度低等缺点,限制了其实际应用。综述了对磷酸铁锂材料改性研究的最新进展,并预测今后的发展方向。     

Cubic NaSbS2 as an Ionic–Electronic Coupled Semiconductor for Switchable Photovoltaic and Neuromorphic Device Applications

The recent emergence of lead halide perovskites as ionic–electronic coupled semiconductors motivates the investigation of alternative solution-processable materials with similar modulatable ionic and electronic transport properties. Here, a novel semiconductor—cubic NaSbS₂—for ionic–electronic coupled transport is investigated through a combined theoretical and experimental approach. The material exhibits mixed ionic–electronic conductivity in inert atmosphere and superionic conductivity in humid air. It is shown that post deposition electronic reconfigurability in this material enabled by an electric field induces ionic segregation enabling a switchable photovoltaic effect. Utilizing post-perturbation of the ionic composition of the material via electrical biasing and persistent photoconductivity, multistate memristive synapses with higher-order weight modulations are realized for neuromorphic computing, opening up novel applications with such ionic–electronic coupled materials.     

高镍三元正极材料的包覆与掺杂改性研究进展

随着新能源汽车的加速发展, 镍钴锰/铝酸锂三元正极材料、特别是高镍(镍含量大于50%)材料作为后起之秀, 由于其性能和成本的综合指标优于传统的钴酸锂和磷酸铁锂, 引起了学术界和产业界极大的研究兴趣。但是受其本身晶体结构和表面结构的限制, 三元正极材料也存在安全性较差、循环稳定性不足等缺点。近年来, 科研工作者为解决这些问题、并进一步提升三元材料的性能, 在材料改性技术方面开展了大量工作, 取得了令人瞩目的研究成果。本文从改性元素对三元正极材料结构以及对电化学性能改善的机理出发, 介绍了包覆和掺杂两种改性技术的研究进展, 并在此基础上对三元正极材料的发展方向做出展望。     

三元FeCl3-AlCl3-GIC的制备及其插层反应过程的研究

采用混合熔融盐法制备以天然鳞片石墨作宿主、以FeCl3和AlCl3为插层剂的GIC。通过考察反应温度、碳与金属氯化物的摩尔比以及保温时间对产物阶结构的影响，探讨了FeCl3和AlCl3在石墨层间的插层反应过程。实验结果表明：调节和控制插层反应条件，可以得到一阶FeCl3-GIC和一阶AlCl3-GIC相对含量不同的三元FeCl3-AlCl3-GIC。插层过程中存在通过生成中间产物AlFeCl6，以FeCl3逐渐替换AlCl3的插层反应机制。替换量随插层反应温度的升高、保温时间的延长和碳与金属氯化物的摩尔比的降低而增大。     

Electrochromic materials and devices: Brief survey and new data on optical absorption in tungsten oxide and nickel oxide films

Current work on inorganic electrochromic materials and devices is reviewed briefly, and the emphasis on thin films of W oxide and Ni oxide is pointed out. New results are presented on the optical properties for sputter-deposited thin films of these two materials: for Li⁺ intercalated sub-stoichiometric W oxide, it is shown that the absorption can be reconciled with an extended “site saturation” model accounting for electronic transitions between W ions in 6+, 5+, and 4+ states, and for H⁺ deintercalated Ni oxide, it is found that the coloration efficiency is higher than in prior work presumably as a consequence of the nanocrystalline structure ensuing from the deposition conditions.     

Synthesis,Al~(3+)/Mg~(2+) Intercalation and Structure Study of Graphite-like Carbon Nitride

Graphite-like carbon nitride(g-C3N4) was synthesized in large quantities at 300 C under nitrogen by a solidstate reaction route.Furthermore,Al3+ and Mg2+ intercalation of g-C3N4 was performed by an electrochemical method.The starting C3N4 materials and intercalation compounds were characterized by X-ray powder diffraction,Fourier transform infrared spectra,thermogravimetry,transmission electron microscopy,and X-ray photoelectron spectroscopy.The possible structure model of intercalation compounds was proposed.The cation-π interactions and electrostatic interactions were used to explain the changes of microstructure and chemical bonds before and after intercalation.     

熔融盐法合成锂离子电池正极材料的研究进展

熔融盐法是利用熔融盐作反应物或兼作熔剂,在固液态间进行反应,可以有效降低反应温度和缩短反应时间,合成出符合计量比以及结晶发育良好的正极材料,是一种合成锂离子正极插层材料的新的有效方法.就国内外采用熔融盐法合成锂离子电池正极材料的现状,结合我们的研究情况进行了综述.     

超薄材料电催化CO_(2)还原合成液体燃料EI北大核心CSCD

电催化CO_(2)还原反应(CO_(2)RR)不仅可以减轻过量CO_(2)造成的负面影响,而且生成的含碳燃料有利于缓解能源短缺。但是,CO_(2)RR路径较为复杂,存在着选择性低、电流密度低和稳定性差等问题,亟需开发高效廉价的催化剂来推进其发展。超薄材料具有大的比表面积、充分暴露的活性位点、加快的动力学传质和可调的电子结构等优势,有望突破CO_(2)RR的研究瓶颈,因此备受关注。本文总结了近4年来不同超薄催化剂的合成及其在电催化CO_(2)还原产液体燃料(甲酸、甲醇、乙酸)中的应用,探讨了超薄材料相较于块体材料的优势及其对催化活性、选择性以及反应路径的影响,并针对未来的发展趋势提出一些建议,包括超薄催化剂的合成方法学、作为载体的潜力、机理分析和机器学习。     

EPR and mixed electronic-ionic conductivity studies of pure and manganese doped layered Potassium–Lithium tetra titanates (K1.9Li0.1Ti4O9)

Lithium (5%) mixed layered K₂Ti₄O₉ and its 0.01, 0.02, 0.05, 0.1 and 1.0 molar percentage MnO₂, doped derivatives have been prepared and characterized through electrical conductivity studies in the temperature range 373–900 K and room temperature EPR investigation. Three distinct regions have been identified in the Log(σT) versus 1000/T plots. The lowest temperature region is attributed to electronic hopping conduction (except for K_1.9Li_0.1Ti₄O₉ (PLT) in which interlayer lithium ionic conduction is proposed) involving loose electrons from Ti₄O₉²⁻ groups. The intermediate region to associated interlayer ionic conduction through dilated interlayer space and the highest temperature region to unassociated interlayer ionic conduction. The room temperature EPR investigations reveal that at a lower percentage of doping the substitution of manganese ions occur as Mn⁴⁺ at Ti⁴⁺ sites, whereas for higher percentage of doping Mn²⁺ ions predominantly occupy the two different interlayer alkali sites. The dilation of interlayer space has further been proposed to occur due to manganese ions substitution at octahedral Ti⁴⁺ sites. In both these cases the charge compensation mechanism should operate to maintain the overall charge neutrality of the lattice.     

Printed transparent electrodes containing carbon nanotubes for elastic circuits applications with enhanced electrical durability under severe conditions

Organic composites filled with nanostructures are new group of materials with unique physical properties. Carbon nanotubes (CNTs) are demonstrating good electrical and mechanical properties. This enables to produce conductive polymer-CNT thick films optically transparent, which are highly useful in production of printed electronic paper. Currently used indium tin oxide (ITO) and antimony tin oxide (ATO) films exhibit high optical transmittance with reasonable electrical conductivity, but very low resilience to mechanical stresses. This is one of the key problems in fabrication of flexible electronic displays. Current authors’ achievements include fabrication of transparent electrodes obtained by screen printing technique, used for production of fully functional thick film electroluminescent structures.